The Mexican Cessions
The cries of manifest destiny and the All Mexico Movement they inspired (as in the earlier All Oregon movement) did not succeed in bringing about the annexation of all Mexico. Nor had they succeeded in acquiring all of Oregon. The compromise with the British over Oregon was to avert the threat of war, the compromise with the Mexican government was with a defeated enemy. US Peace Commissioners did not insist on annexation of the territories held by US Armies in Mexico. Instead they concentrated on the lands which now make up the American Southwest. The Mexican Cessions were the third largest land acquisition in American history, following the Louisiana Purchase and the Alaska Purchase.
The vehicle through which the cessions occurred was the 1848 Treaty of Guadalupe Hidalgo. The territories which were ceded to the United States in the treaty were sparsely populated for the most part, which made the treaty acceptable to the southerners who had argued against allowing non-whites American citizenship by annexation. Its vast lands, including all of California, meant that the United States controlled all of the territory which would eventually become the contiguous forty eight states, after some border adjustments negotiated through other treaties. For fervent proponents of manifest destiny, America’s victory and the cession of the Mexican lands was proof of the concept.
The language of the treaty did not openly cede the lands to the United States, instead it redefined Mexico’s border with the United States. This allowed the cession to appear as voluntary, rather than the United States seizing the land by right of conquest. Mexico was compensated for the land by $15 million when the Senate ratified the Treaty. The compensation did not transfer any money to Mexico, instead it was credited to Mexico’s debt to the United States, part of which was from allowing itself to be defeated by the Americans during the war. Since 1821, when Mexico became independent from Spain, 54% of its territory had been lost to the United States.
The seizure of the formerly Mexican lands exacerbated the growing issue of abolitionism in the United States, and for the next decade America drew ever closer to Civil War. The issue of whether states and territories formed from the newly acquired lands should be slave or free led to increasingly hostile debate in Congress, raised further by the strident voices of the abolitionists in the North, and state’s rights advocates of the South. Only a year following the Treaty of Guadalupe Hidalgo, gold was discovered in California, to be followed by the fabulous silver strikes in Nevada. California became a state in 1850. Settlers streamed to the west.
America’s manifest destiny proponents were not silent in the debate over slavery, with those of the North believing that manifest destiny applied to the slave states as it did to the unsettled lands of the west. Settlement of the formerly Mexican lands began immediately, where it was opposed by the residents already there, the American Indians. In some areas of the United States, but very few, Indians had been assimilated into the population. The western tribes were something Americans, other than trappers and explorers, had not encountered before, more nomadic, and less reliant on grown crops as those of the east had been. Manifest destiny would soon affect them too.